-LRB- CNN -RRB- -- Israel 's attack Monday on a boat traveling in international waters and carrying humanitarian supplies for Gaza killed at least nine people and sparked a series of recriminations around the world .

Riyad Mansour , Palestinian ambassador to the United Nations , condemned the attack and called for an independent investigation `` to know who gave the orders from the Israeli side to open fire against civilians and to bring those people to face justice . ''

But Israeli officials described the boat 's passengers as the aggressors and said the soldiers from the Israel Defense Forces were simply defending themselves .

`` They are not peace activists . They were not messengers of goodwill , '' Daniel Carmon , Israel 's deputy ambassador to the United Nations , told reporters in New York . `` They cynically used the guise of humanitarian aid to send a message of hate and to implement violence . ''

Independent information was scant . The death toll and the account of what happened came from the Israelis , who did not release the names of any of the casualties . `` Free Gaza , '' one of the group 's sponsors , said there were more casualties from the incident , though it did n't have an exact number .

The surviving passengers were being held incommunicado by the Israelis , who detained them after escorting the six boats that had participated in the flotilla to the Israeli port city of Ashdod .

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Three sailors who took part in the flotilla said Israeli troops stormed the Mavi Marmara , the largest ship , well into international waters .

`` The commandos were coming down from the helicopter . No one on the ships had any weapons , '' one of the sailors told CNN Turk after being flown back to Istanbul .

The Free Gaza organization , one of the organizers of the protest , posted on its Twitter page that the incident unfolded about 4:30 a.m. , when Israeli commandos boarded the Mavi Marmara by helicopter . The troops `` immediately opened fire on unarmed civilians , '' the group said .

Video from the Israeli military showed soldiers rappelling onto the deck of the ship from a helicopter . The boarding of the ships took place in international waters more than 70 nautical miles -LRB- 130 km -RRB- outside Israeli territorial waters , according to IHH , a humanitarian relief foundation and a sponsor of the flotilla . IHH is affiliated with the Muslim Brotherhood , a hard-line Islamic political movement .

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But the Israel Defense Forces said its troops `` were met with premeditated violence , evident by the activists ' use of clubs , metal rods , and knives , as well as the firing of two weapons stolen from the soldiers . '' It said troops responded with `` defensive action on behalf of the forces who felt their lives were endangered , '' and seven were wounded .

The IDF released a video shot from above the ship that it said showed soldiers being attacked , though the distance from which it was shot precluded immediate confirmation . A senior Israeli military official , speaking on condition of anonymity in an account cleared by military censors , displayed a box containing switchblade knives , slingshots and metal balls and bats he said had been confiscated from one of the boats .

`` This was not spontaneous , '' he said . `` This was planned . ''

Israeli military gives version of flotilla incident

A senior Israeli military official , speaking on condition of anonymity in an account cleared by military censors , displayed a box containing switchblade knives , slingshots and metal balls and bats he said had been confiscated from one of the boats .

`` This was not spontaneous , '' he said . `` This was planned . ''

Jonathan Peled , minister-counselor for the Israeli Embassy in Washington , said the soldiers were carrying paintball pistols when they boarded the flotilla , but switched to bullets when a naval commander was stabbed and others were attacked with knives and metal bars .

Most of the dead were Turks , the Israeli senior military official said . Twenty other people were wounded .

As many as nine Americans may have been aboard the boats , including Edward Peck , a former U.S. ambassador to Mauritania , according to Jonathan Slevin , a spokesman for the activist group Free Palestine Movement .

One American who was being treated for minor injuries after the attack , a senior State Department official said late Monday .

Israeli forces boarded the other ships in the flotilla without incident . The Turkish sailors said they were continuously shadowed by commandos aboard their own vessel , `` even when we needed to go to bathroom , '' one said .

The flotilla had left European ports in a protest organized by two pro-Palestinian groups to deliver 10,000 tons of food , medicine , construction materials , wheelchairs and other aid to Gaza to break a blockade imposed by Israel in 2007 .

Israeli Prime Minister Benjamin Netanyahu , who canceled his trip to Washington to return to Israel to manage the crisis , said Gaza has become a base for Hamas terrorists who have fired `` thousands of rockets '' into Israel .

`` What we want to prevent coming into Gaza are rockets , missiles , explosives and war material that could be used to attack our civilians , '' he told reporters in Ottawa , Canada , with his Canadian counterpart .

The attack sparked protests in several countries ; caused a diplomatic row between Israel and Turkey , its closest Muslim ally ; and brought condemnation worldwide . A number of nations recalled their ambassadors from Israel , while others called for a full investigation .

The Palestinian Authority said in a statement its cabinet `` strongly condemned the Israeli crime against international supporters on board of the Freedom Flotilla . ''

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Turkey , Israel 's closest Muslim ally in the region , recalled its ambassador , while Deputy Prime Minister Bulent Arinc said the operation `` will leave a bloody stain on the history of humanity . ''

Israel said Sunday that Western and Turkish authorities have accused IHH of having `` working relations '' with terrorist organizations .

Of the hundreds of activists who were detained aboard the ships after they were escorted to the Israeli port of Ashdod , 15 were sent to Beer Sheva Prison , according to a spokesman for the Israeli prison authority . Another 25 were slated for deportation and 50 others who refused to identify themselves were being held separately .

None was allowed to speak to the news media .

A team from the Turkish Red Crescent will fly Tuesday to Tel Aviv to help coordinate the return of the dead and wounded , the organization said in a statement .

Israel issued a `` serious travel warning '' for Israelis visiting Turkey . Those planning to travel to Turkey were asked to postpone their trips , while those already in Turkey were advised to stay indoors . A Turkish travel agent said more than 15,000 Israelis had canceled plans to visit Turkey .

In Gaza , Hamas spokesman Sami Abu Zuhri called for global support of the Palestinian cause . Palestinian Authority President Mahmoud Abbas called for three days of mourning in the Palestinian territories to honor the lives lost .

`` We have consistently advised against attempting to access Gaza in this way , because of the risks involved , '' said British Foreign Secretary William Hague . `` But at the same time , there is a clear need for Israel to act with restraint and in line with international obligations . ''

In Washington , White House spokesman Bill Burton said , `` The United States deeply regrets the loss of life and injuries sustained and is currently working to understand the circumstances surrounding this tragedy . ''

Israel instituted a blockade on Gaza in January 2006 , when Hamas won democratic elections in the Palestinian territories . It tightened that blockade in June 2007 , when Hamas took over Gaza , but allows about 15,000 tons of humanitarian aid into the territories each week , Israeli government spokesman Mark Regev said .

Since then , Israel has controlled entry of all manner of goods into Gaza , including instant coffee , chocolate and construction materials . Israel has said the latter could be used by Hamas to build bunkers .

Since the summer of 2008 , five flotillas have gotten through the blockade to deliver humanitarian goods to Gaza . Monday 's flotilla was the largest such mission .

CNN 's Ben Wedeman in Cairo , Egypt ; Ivan Watson in Istanbul , Turkey ; Charley Keyes in Washington ; and Niki Cook in Paris , France , contributed to this report .

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NEW : As many as nine Americans may have been aboard ship , activist says

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9 dead in flotilla clash between activists , Israeli military

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Israel insists troops were defending themselves

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